1. Field of the Invention
This invention relates to a protective device and circuitry for use in conjunction with input and output test and calibration terminals of electronic instruments.
2. Description of the Prior Art
Electronic instruments are widely used for purposes of translating physical variables to be operated upon into electrical signals and transmitting these electrical signals over a distance to an electrical device of known type. Such instruments are common in the chemical, petroleum, metals and mining industry to name but a few such industries. These transmitted electrical signals are normally used to indicate display, record and/or monitor, in conjunction with additional equipment, the physical quantities represented by the transmitted electrical signals. Often, the input signals to the many electrical instruments are initially electrical in nature such as those derived from thermocouples, resistance temperature detectors (RTDs) and other physical variable transducers. The reliability of performance and faithfulness of signal acquisition and transmission is of great importance and is enhanced by the rigid mounting of the instruments to substantial support structures. It has also been the practice to secure wires from external devices to the electronic instrument by means of screw terminals to maximize the integrity of the connection and to minimize alteration of the signal being received at the securing site.
Furthermore, the accuracy of the electronic instruments often comes into question and, in this situation, it is desirable to calibrate the instrument for accuracy and make adjustments, if necessary, to ensure maximum accuracy. When such calibration takes place in instruments of the type described above, because of the solid mounting of the instruments and the screw attachment of the wires, the removing and later remounting of an instrument is a time-consuming matter. The invention to be described hereinbelow relates to this problem wherein screw attached wires need not be disattached for calibration purposes. Also, access to the instrument is provided without the requirement of removing the instrument from its rigid mounting support.